We’ve defined microevolution as a change in gene frequency in a population and a population as a group of organisms that share a common gene pool—like all the individuals of one beetle species living on a particular mountaintop.

Macroevolution generally refers to evolution above the species level. So instead of focusing on an individual beetle species, a macroevolutionary lens might require that we zoom out on the tree of life, to assess the diversity of the entire beetle clade and its position on the tree.

Evolution is defined as variation in the frequencies of alleles, where an allele is a specific iteration of a given gene. Microevolution is defined as variations in the frequencies of alleles below species level, in a population of organisms. Macroevolution is defined as variations in the frequencies of alleles at or above species level, or in populations of populations. The easiest way to think about this is that evolutionary biologists study frequencies of alleles that are shared between two species so, for example, there are many genes that are shared between humans and chimpanzees, which is to say that humans and chimps carry exactly the same version of the gene.

Another useful example is extinction, in which the frequency of all alleles in a species go from some to none.

What the creationist is actually talking about here is something that would falsify evolutionary theory wholesale, namely a cat giving birth to a dog. This, of course, doesn't happen. What does happen, though, is speciation, and in fact there is a beautiful example of extinction and speciation in a single event, namely an extinction event in a ring species. If a selection of sub-species in the middle of the ring go extinct, by a bolide impact, for example, and the remaining subspecies are no longer reproductively compatible, then we have an extinction event that is also a speciation event, both of which are correctly defined as macroevolution.

I don't understand how there could be any difference between micro and macro evolution. Surely any life form large enough to contain genes would evolve in exactly the same way? The genes don't really care how big an organism is going to grow. Their job is simply to provide the blue print for the morphology of the animal. Look at a great Dane and a chihuahua. And consider how the size of closely related species has altered over time ex horses getting progressively larger while elephants get smaller. Some plankton remain microscopic all their lives while others grow into giant squid. Size is not that much of an issue. It is a temporary characteristic of a species and can rapidly change with the availability of food.